Combined effects of metal and ligand capable of accepting a proton or hydrogen bond catalyze anti-Markovnikov hydration of terminal alkynes

Article abstract of DOI:10.1002/1521-3773(20011015)40:20<3884::AID-ANIE3884>3.0.CO;2-7

A binding pocket for water is created in 1 by the imidazolyl phosphane ligands and the Ru¹¹ center. Compound 1 proves to be an excellent catalyst for a highly selective anti-Markovnikov hydration of terminal alkynes to give aldehydes rather than isomeric ketones under near-neutral conditions (aldehyde-to-ketone ratio up to 1000:1).

Full text of DOI:10.1002/1521-3773(20011015)40:20<3884::AID-ANIE3884>3.0.CO;2-7

COMMUNICATIONS
[4] a) Hybrid Organic-Inorganic Composites, Vol. 585 (Eds.: J. E. Mark,
C. Y-C. Lee, P. A. Bianconi), American Chemical Society, Washing-
ton, DC, 1995; b) special issue on nanostructured materials; Chem.
Mater. 1996, 8(8), and references therein; c) R. Gangopadhyay, A. De,
Chem. Mater. 2000, 12, 608; d) K. G. Sharp, Adv. Mater. 1998, 10, 1243;
e) P. J. Hagrman, D. Hagrman, J. Zubieta, Angew. Chem. 1999, 111,
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Nazar, Solid State Ionics Diffusion and Reactions 1996, 89(1 ± 2), 147.
[5] a) E. Potiron, A. Le Gal La Salle, A. Verbaere, Y. Piffard, D.
Guyomard, Electrochim. Acta 1999, 45, 197; b) E. Potiron, A.
Le Gal La Salle, S. Sarciaux, Y. Piffard, D. Guyomard, J. Power
Sources 1999, 81, 666.
Combined Effects of Metal and Ligand Capable
of Accepting a Proton or Hydrogen Bond
Catalyze Anti-Markovnikov Hydration of
Terminal Alkynes**
Douglas B. Grotjahn,* Christopher D. Incarvito, and
Arnold L. Rheingold
Metalloenzyme catalysts such as carboxypeptidase use the
cooperative effects of a metal ion and suitably placed organic
functional groups capable of proton transfer or hydrogen
bonding.[1, 2] Using this cue from Nature, we are making
complexes of general structure A (Scheme 1) where L is a
[6] a) Y. J. Liu, D. C. DeGroot, J. L. Schindler, C. R. Kannewurf, M. G.
Kanatzidis, Chem. Mater. 1992, 3, 992; b) Y. J. Liu, J. L. Schindler,
D. C. DeGroot, C. R. Kannewurf, W. Hirpo, M. G. Kanatzidis, Chem.
Mater. 1996, 8, 525.
[7] a) F. Leroux, G. R. Goward, W. P. Power, L. F. Nazar, J. Electrochem.
Soc. 1997, 144, 886 ± 3895; b) F. Leroux, B. E. Koene, L. F. Nazar, J.
Electrochem. Soc. 1996, 143, L181 ± 182.
[8] a) S. Wong, S. Vasudevan, R. A. Vaia, E. P. Giannelis, D. Zax, J. Am.
Chem. Soc. 1995, 117, 7568; b) M. M. Doeff, J. S. Reed, Solid State
Ionics Diffusion and Reactions 1998, 113 ± 115, 109.
[9] a) K. Salloux, F. Chaput, H. P. Wong, B. Dunn, J. Electrochem. Soc.
1995, 142, L191; b) D. B. Le, S. Passerini, A. L. Tipton, B. B. Owens,
W. H. Smyrl, J. Electrochem. Soc. 1995, 142, L102; c) F. Coustier, S.
Passerini, W. H. Smyrl, J. Electrochem. Soc. 1998, 145, L73; d) F.
Coustier, J.-M. Lee, S. Passerini, W. H. Smyrl, Solid State Ionics 1999,
116, 279.
[10] P. Liu, J-G. Zhang, C. E. Tracy, J. A. Turner, Electrochem. Solid-State
Lett. 2000, 3, 163.
[11] Data obtained in a voltage window of 4 ± 1.5 V, with only 1 mgcm 2 of
active material in the film, at a rate of 5 C. The latter refers to
discharge or charge of 1Li in 1/5 of an hour.
[12] a) Y. Choquette, M. Gauthier, C. Michot, M. Armand, Canadian
Patent CA2248304 1998; b) N. Tsubokawa, Prog. Polym. Sci. 1992, 17,
417; c) J.-H. Lin, H.-W. Chen, K.-T. Wang, F.-H. Liaw, J. Mater. Chem.
1998, 8, 2169.
Ph2P
LnM
O
L
Me
N
N
Me
a
N
N
N
H
H
1
2
A
CF3SO3
CF3SO3
Ru
Ru
Me
Ph2P
NCCH3
PPh2
CH3CN
Me
NCCH3
N
O
b
N
H
H
+
+
H2O
N
2
3
N
(molar ratio 2 : 1 : 5)
4
Scheme 1. Design (A) and synthesis of catalyst 4. a) nBuLi, THF, 78 to
508C, 3 h, then ClPPh2, warming to RT, 51%; b) CDCl3 or CH2Cl2, RT,
<2 h, 98%.
[13] Carbon black: science and technology (Eds.: J.-B. Donnet, R. C.
Bansal, M.-J. Wang), Marcel Dekker, New York, 1993.
[14] J. Lemerle, L. Nejem, J. Lefebvre, J. Chem. Res. 1978, 5301; J. Livage,
Chem. Mater. 1991, 3, 578.
ligating atom and N is part of a heterocycle, particularly
imidazole. Our results clearly indicate that the combined
effects of a metal and a proton or hydrogen bond acceptor as
in A produce a binding pocket for a polar ligand. We report
herein on the anti-Markovnikov hydration of terminal
alkynes [Eq. (1)], which produces aldehydes, rather than the
isomeric ketones, with selectivities of up to 1000 to 1.
[15] IR spectra of V2O5/C-PEG products showed three strong vibrations at
1000, 760, and 521 cm 1, identical to those of V2O5 xerogel. In the CH2
stretching absorption region, the strong band at 2877 cm 1 observed in
bulk PEG is split into two bands at 2924 and 2854 cm 1. In the region
1500 ± 1000 cm 1, no significant energy shifts were observed with
respect to bulk PEG, but the relative intensities of the absorption
bands were different and the band shapes were broader. The XRD
and IR results confirmed that PEG was inserted into the V2O5 layers,
and the insertion did not affect the structural integrity of the V2O5
framework.
O
R
CH3
[16] Chemical composition for x(Li) for all materials were calculated from
the formula weight of the materials determined by thermogravimetric
and chemical analyses [%]; for V2O5/C-PEG: V2O5: 72.5, C: 12.1,
PEG: 6.03; for V2O5/C: V2O5: 72.1, C: 16.6.
2% 4
C
O
C
R
R
C
C H
not
(1)
CH2
H
+ H2O
(5 equiv)
acetone,
70 oC
anti-Markovnikov Markovnikov
product product
[*] Prof. D. B. Grotjahn
Department of Chemistry
San Diego State University
5500 Campanile Drive
San Diego, CA 92182-1030 (USA)
Fax : (‡1)619-594-4634
E-mail: grotjahn@chemistry.sdsu.edu
C. D. Incarvito, Prof. A. L. Rheingold
Department of Chemistry and Biochemistry
University of Delaware
Newark, DE 19716 (USA)
[**] The support of San Diego State University is acknowledged.
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
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COMMUNICATIONS
Traditional methods of hydrating alkynes require catalysis
by strong acids and environmentally objectionable HgII, or
transition metal salts. All of these conditions give Markovni-
kov addition of water to the terminal alkyne, leading to the
formation of the methyl ketone.[3±9] Anti-Markovnikov hydra-
tion can be achieved indirectly by stoichiometric hydrobora-
tion or hydrosilation, followed by oxidation.[10] Bruneau and
Dixneuf recently reviewed anti-Markovnikov addition of
weak nucleophiles with N H or O H bonds to terminal
alkynes.[11] Thus far, however, there have been only two
reports of catalytic anti-Markovnikov hydration of terminal
alkynes. In 1998, Tokunaga and Wakatsuki[12] found after
trying about 20 phosphanes that the combined use of
[(C6H6)RuCl2(C6F5PPh2)]
(10 mol%)
and
C6F5PPh2
(30 mol%) gave aldehydes in 50 ± 75% yield, with typical
aldehyde-to-ketone selectivities of about 10 to 1. Hindered
alkynes such as phenyl- or tert-butylacetylene gave less than
2% yields of product. This year the same group reported
improved results with chelating or electron-rich, small
phosphanes on the CpRuCl fragment.[13] For example, in
favorable cases 1 ± 2 mol% of [CpRuCl(Me2PCH2PMe2)] or
[CpRuCl(PMe3)2] could be used in 2-propanol/water at
1008C. In some cases 10 mol% of catalyst was needed,
moreover nitriles inhibit the reaction.
In contrast, here we report that electron-rich phosphanes
are not needed. Significantly, hydrogen bonding in catalyst 4
(Scheme 1) leads to hydration of even tert-butylacetylene at
the 2 mol% level, giving yields in excess of 90%. Advantages
of 4 over the other RuII catalysts reported include a lack of
inhibition by nitriles, and the tolerance of acid-sensitive
propargylic ether substituents.
Figure 1. X-ray crystal structure of the cation of 4 (thermal ellipsoids are at
30% probability). The CF3SO3 counterion is not shown for clarity. Key
bond lengths [Š] and angles [8]: Ru(1)-O(1) 2.164(3), Ru(1)-P(1)
2.3043(10), Ru(1)-P(2) 2.3251(10), Ru(1)-Cp(centroid) 1.836(4), N(2)-H
1.802(8), N(4)-H 1.638(6); P(1)-Ru(1)-P(2) 97.77(3), P(1)-Ru(1)-O(1)
93.30(9), P(2)-Ru(1)-O(1) 91.89(8).
Table 1. Catalysis of alkyne hydration [see Eq. (1)].[a]
Entry Catalyst
Alkyne
substituent
R
Aldehyde yield [%]
after reaction time
Selectivity[b]
3 h
21 h
later [h]
1
2
3
4
5
6
7
8
9
10
11
12
13
4
4
4
4
4
4
4
4
Bu
39
92
88
21
20
64
91
83
96
96 [36]
92 [46]
91[c]
1000
150
PhCH2CH2
(CH3)3C
Ph
Ph[e]
TBSO-CH2
THPO-CH2
40
3.5
9.6
24
28
35
34
0.1
0.3
< 0.1 < 0.1
ꢀ 130
54[d]
135
75 [42]
96 [36]
86 [50]
98 [40]
n.d.
n.d.
n.d.
n.d.
1.2[i]
32
[f]
ꢀ 200
ꢀ 400
n.d.[h]
n.d.
n.d.
n.d.
[g]
Pursuing the design outlined above, we made the phosphi-
noimidazole ligand 2 (Scheme 1) by deprotonation of 1[14, 15] at
C-2, followed by quenching with ClPPh2.[16] We found that two
moles of 2 rapidly react with 3[17] in the presence of five
equivalents of water to give (after crystallization) a 98% yield
NC(CH2)3
5
6
Bu
Bu
Bu
0.3
0.5
6 ‡ 1
6 ‡ Et3N Bu
0
0.3
0
1.0
n.d.
n.d.
7
Bu
1
of catalyst 4. The presence of a H NMR signal near d ˆ 9.1
[a] Conditions: 0.5 mmol alkyne, 5 equiv water, 2 mol% catalyst, and
(Me3Si)4C internal standard in [D6]acetone (1 mL) heated in a sealed NMR
tube in an oil bath (67 ± 728C). Yields and products identified by 1H and in
some cases 13C NMR data. See Supporting Information for full details.
[b] Ratio of aldehyde (value shown) to ketone (assigned value of 1).
Authentic sample of ketone added at end of reaction period. See
Supporting Information for full details. [c] Yield 49% after 68 h; 91%
after an additional 108 h at 88 ± 918C. [d] Yield 54% after three additions
of 2 mol% 4 and 36 ± 45 h heating each time. [e] Using 10 mol% catalyst
with substrate concentration of 0.2m. [f] TBS ˆ (CH3)2(tBu)Si. [g] THP ˆ
3,4,5,6-tetrahydropyran-2-yl. [h] n.d. ˆ not determined. [i] After 7 d at
908C.
(slightly broad singlet, 2H, H2O ± Ru) and satisfactory
elemental analysis suggested that a water molecule was
indeed coordinated to the metal center. However, unequiv-
ocal verification of the water molecule in the catalyst binding
pocket was provided by an X-ray crystal structure determi-
nation (Figure 1).[18] A piano-stool structure supports the cis
coordination of the two phosphane ligands (P-Ru-P angle
97.77(3)8), the third leg of the stool consisting of the Ru O
bond (P-Ru-O angles 91.89(3) and 93.30(9)8). Of special
interest for catalyst design, both (located) hydrogen atoms of
the bound water molecule engage in hydrogen bonding to the
two imidazoles, with N ´´´ H distances of 1.638(6) and
1.802(8) Š.
an authentic sample was added. A very small peak increased
in size, such that we estimate that only 0.1% of 2-hexanone
had been present before addition of authentic material,
meaning that the aldehyde-to-ketone ratio was 1000 to 1. Our
results compare favorably with those of Tokunaga and
Wakatsuki with the same alkyne.[12, 13] Moreover, Table 1
shows that 4 works with a wide variety of substrates, giving
high selectivities. Alkyl-substituted alkynes work the best
(Table 1, entries 1 ± 3, 6 ± 8). A tert-butyl group (Table 1,
entry 3) slows hydration but on heating at 88 ± 918C,
Gratifyingly, only 2 mol% of complex 4 catalyzed the clean
conversion of 1-hexyne (Table 1, entry 1) to hexanal at
temperatures near 708C. Reaction progress was monitored by
1H NMR spectroscopy by using an internal standard. Within
1.5 days, consumption of alkyne was complete, and hexanal
had been formed in 96% yield. NMR spectroscopy showed
that about half the catalyst remained intact. No peaks for the
Markovnikov product 2-hexanone were evident in the
1
500 MHz H NMR spectra, but to verify this result, 1% of
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trimethylacetaldehyde is formed in 91% yield. Phenylacet-
ylene reacts about as sluggishly as tert-butylacetylene, but in
this case NMR spectroscopy confirms that 2 mol% 4 (Table 1,
entry 4) disappears after 21 h and hydration stops at about
30% conversion unless additional catalyst is added, even-
tually producing 54% aldehyde. Alternatively (Table 1,
entry 5), starting with 10 mol% 4, improved yield and rate
are obtained.
such as alkyne, vinylidene (C), hydroxycarbene (D), or
related, tautomeric acyl and hydride (E).[23] Any of the
conversions between these species conceivably could be aided
by the presence of the imidazole groups or their protonated
forms (e.g., F).[24] Alternatively, the hydrogen bonding in 4
may stabilize the catalyst. Judging from the lack of catalytic
reactivity of other {CpRu(PAr3)2} fragments under the con-
ditions used (e.g., Table 1 entries 9 ± 13 and ref. [23b]), the
effects of R ˆ imidazol-2-yl are especially intriguing and are
the subject of ongoing studies. We note that the most recent
CpRuCl-based catalyst was inhibited by a nitrile-containing
alkyne;[13] the lack of inhibition of 4 may be related to the
ability of 4 to exclude a coordinated nitrile in its resting state
(A, Scheme 2).
In conclusion, regardless of mechanism, we provide clear
evidence that the combined effects of a RuII center and
imidazolylphosphanes create an excellent single-component
catalyst for the anti-Markovnikov hydration of terminal
alkynes under near-neutral reaction conditions. We are
currently extending our design principle to other structures
and reactions.
A nitrile does not affect the catalyst (compare entries 8 and
1 in Table 1). Even alkynes with acid-sensitive alcohol
protecting groups (Table 1, entries 6 and 7) are hydrated to
give aldehydes made previously in multistep syntheses.[19]
Remarkably, neither an allenylidene complex nor propargyl
alcohol (a potential hydrolysis product) are formed.[20]
Several control experiments show that the imidazole groups
play a key role in the catalysis. First, in hydration of 1-hexyne,
simple triarylphosphane ligands of slightly different electronic
‡
properties on the [CpRu] ion (5 and 6; Table 1, entries 9 and
CF3SO3
Ru
Ru
PAr3
PAr3
PPh3
CH3CN
Cl
PPh3
5 PAr3 = PPh3
6 PAr3 = P(4-ClC6H4)3
Experimental Section
7
Preparation of catalyst 4: Deoxygenated solvents were used in an M. Braun
glovebox. To solid phosphane 2 (120.0 mg, 0.372 mmol) and [CpRu(CH3C-
N)3OSO2CF3] (3; 78.3 mg, 0.179 mmol) was added CH2Cl2 (3 mL). Water
(16 mL, 0.89 mmol) was added and the resulting solution was stirred for 2 h
before being concentrated in vacuo. The residual orange gum was dissolved
in acetone (2 mL) containing water (16 mL) and the resulting solution
transferred to a tared vial. The vial was placed in a small jar containing
hexanes. After one day, crystals of 4 had formed and the supernatant was
removed from them by pipet. The crystals were rinsed with hexanes and
placed under vacuum, leaving orange crystals and powder (172.2 mg, 98%
10, respectively) give less than 0.5% yields of hexanal, with no
2-hexanone being detected.[21] Further, if the imidazole groups
function merely as a base, their placement in 4 is crucial:
addition of 2 mol (per Ru center) of either the hindered
imidazole base 1 or Et3N to mixtures containing 6 led to
virtually no production of aldehyde (Table 1, entries 11 and
12). Finally, complex 7 is also ineffective (Table 1, entry 13).
As to the probable mechanism of the alkyne hydration,
ketones may come from attack of water on C-2 of alkyne p
complexes (B, Scheme 2).[22] In contrast, for aldehyde for-
mation, likely intermediates include complexes with ligands
1
yield). H NMR ([D6]acetone, 500 MHz): d ˆ 9.12 (sl br s, 2H), 7.54 ± 7.58
(m, 4H), 7.49 ± 7.54 (m, 2H), 7.32 ± 7.41 (m, 6H), 7.17 (s, 2H), 7.13 (sl br t,
J ˆ 7.5 Hz, 4H), 7.01 (sl br dd, J ˆ 8.5, 10 Hz, 4H), 4.19 (s, 5H), 2.85 (s, 6H),
1.36 (s, 18H); 31P{1H} NMR (CDCl3, 80.95 MHz): d ˆ 26.72 (br s);
elemental analysis (%) calcd for C46H53F3N4O4P2RuS (978.03): C 56.49, H
5.46, N 5.73; found: C 56.39, H 5.21, N 5.79.
Example of procedure used to monitor alkyne hydration: Conversion of
4-phenyl-1-butyne to 4-phenylbutanal (Table 1, entry 2): In the glovebox,
catalyst 4 (9.8 mg, 0.010 mmol) and internal standard (Me3Si)4C (0.5 mg)
were added to a vial. Using portions of [D6]acetone (total volume 0.7 mL),
the solid complex and standard were transferred by pipet to a resealable
NMR tube. Not all 4 had dissolved at this point, so the transfer using
solvent was partially mechanical. Water (45 mL, 2.5 mmol) was added,
followed by PhCH2CH2CCH (64.6 mg, 0.496 mmol) and enough [D6]ace-
tone to bring the total volume to 1.0 mL. The tube was sealed, removed
from the glovebox, and briefly placed in a sonicating bath to dissolve all the
LnM
C
L
LnM
C
L
R
C
C
H
N
N
R
C
H
C
B
C
R
H
H2O
1
catalyst to form a pale orange-yellow solution. The H NMR spectrum of
the resulting solution was recorded at this point and at intervals during
heating of the NMR tube, using the same conditions (Varian 500 MHz
spectrometer, four 308 pulses, 120 s delays between pulses). Monitoring
reactions by NMR spectroscopy rather than by GC allowed us to determine
if catalyst was still present. After 46 h, a sample of 4-phenyl-2-butanone
(2 mL, 0.013 mmol, 0.027 times the amount of alkyne added) was added to
the NMR tube. A small singlet (ascribed to the methyl protons of the
ketone) at d ˆ 2.086 grew in size. The increase in the singletꢁs integral
indicated an aldehyde-to-ketone ratio of 150 to 1 before ketone addition.
For the less volatile aldehydes made in entries 6 and 7 in Table 1, the
mixture was worked up to provide pure aldehyde. Full details of these
experiments are available in the Supporting Information.
LnM
C
L
LnM
L
O
R
N
H
C
H
N
H
OH
C
A
H
H
R
D
O
C
H
H
H2O
LnM
C
L
LnM
C
L
H
N
N
R
R
O
O
C
C
H
H
H
H
H
E
or
F
Scheme 2. Probable intermediates and mechanism of alkyne hydration.
Received: May 23, 2001 [Z17165]
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COMMUNICATIONS
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[4] V. Janout, S. L. Regen, J. Org. Chem. 1982, 47, 3331 ± 3333.
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Design and discovery of new catalysts that operate by
nontraditional mechanisms offer the possibility of efficient
and selective transformations that are difficult to achieve by
conventional methods. Reactions proceeding through ionic
mechanisms are attractive targets for development in this
context. The traditional homogeneous catalytic hydrogena-
tion of carbonyl groups[1] involves the coordination of a
ketone or aldehyde substrate to a metal center and insertion
ˆ
of the C O bond into a metal hydride bond. In ionic
hydrogenations, hydrogen gas is heterolytically cleaved by a
metal complex and then added to an unsaturated organic
Â
complexes to transform alkynes, see also S. Derien, L. Ropartz, J.
Le Path, P. H. Dixneuf, J. Org. Chem. 1999, 64, 3524 ± 3531; C.
Slogovc, K. Mereiter, R. Schmid, K. Kirchner, Organometallics 1998,
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2000, 122, 5877 ± 5878.
‡
compound through proton (H ) and hydride (H ) transfer
steps. We recently reported Mo and W catalysts for ketone
hydrogenation that operate by an ionic hydrogenation path-
way under mild conditions.[2] Magee and Norton discovered a
Ru system that catalyzes the enantioface-selective hydro-
[12] M. Tokunaga, Y. Wakatsuki, Angew. Chem. 1998, 110, 3024 ± 3027;
Angew. Chem. Int. Ed. 1998, 37, 2867 ± 2869.
[13] T. Suzuki, M. Tokunaga, Y. Wakatsuki, Org. Lett. 2001, 3, 735 ± 737.
[14] B. H. Lipshutz, M. C. Morey, J. Org. Chem. 1983, 48, 3745 ± 3750.
[15] C. Hilf, F. Bosold, K. Harms, J. C. Lohrenz, M. Marsch, Chem. Ber.
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[16] Conditions used were patterned after N. J. Curtis, R. S. Brown, J. Org.
Chem. 1980, 45, 4038 ± 4040. For synthesis of several analogs of 2, see
D. B. Grotjahn, D. Lev, Y. Gong, G. Boldt, G. Aguirre, Organo-
metallics, manuscript submitted.
[17] D. B. Grotjahn, H. C. Lo, Organometallics 1996, 15, 2860 ± 2862.
[18] For 4 (C46H53F3N4O4P2RuS): monoclinic, P21/n, a ˆ 14.517(3), b ˆ
19.349(4), c ˆ 16.900(3) Š, b ˆ 98.824(19)8, Vˆ 4690.9(15) Š3, Z ˆ 4,
Z' ˆ 1, Tˆ 251(2) K, 1calcd ˆ 1.385 gcm 1, orange block, GOF ˆ 1.184,
R(F) ˆ 0.0525 for 6433 observed independent reflections. Crystallo-
graphic data (excluding structure factors) for the structure reported in
this paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-163304. Copies
of the data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk).
genation of C N bonds by an ionic mechanism.[3] Shvo and co-
ˆ
workers reported a remarkable series of reactions catalyzed
by ruthenium complexes with phenyl-substituted cyclopenta-
dienone ligands,[4] and recent studies by Casey et al. demon-
strated that the proton and hydride transfer are concerted in
such systems.[5] The remarkably reactive Ru hydrogenation
catalysts of Noyori and co-workers are now thought to
proceed by a related mechanism in which H2 is cleaved to
form M H and N H bonds.[6]
Synthetic procedures for deoxygenation of alcohols[7] gen-
erally involve multiple steps and low atom efficiencies.[8]
Selective deoxygenation of one of the two OH groups of diols
presents an even more formidable challenge than the
deoxygenation of alcohols. Vicinal OH functionalities repre-
sent a ubiquitous feature of compounds derived from
carbohydrates, but diols and polyols are unsuitable precursors
for many industrial applications because they are overfunc-
tionalized with an abundance of OH groups of very similar
reactivity. Conversion of biomass to useful industrial chem-
icals[9] offers an attractive solution to consumption of petro-
leum-based resources, an aspect of growing concern. We
[19] For examples, see: A. P. Kozikowski, P. D. Stein, J. Org. Chem. 1984, 49,
Â
2301± 2309; N. Adje, P. Breuilles, D. Uguen, Tetrahedron Lett. 1993, 34,
Â
 Â
4631 ± 4634; I. Berque, P. Le Menez, P. Razon, J. Mahuteau, J.-P. Ferezou,
A. Pancrazi, J. Ardisson, J.-D. Brion, J. Org. Chem. 1999, 64, 373 ± 381.
[20] Y. Nishibayashi, I. Wakiji, M. Hidai, J. Am. Chem. Soc. 2000, 122,
11019 ± 11020.
[21] The phosphane P(4-ClC6H4)3 models the mild electron-withdrawing
character of the imidazole ring compared with phenyl. The electronic
effect of the imidazole substituent was probed using trans-
[Rh(Cl)(CO)(L)2] where Lˆ the N-isopropyl analogue of 2 (D. Grot-
jahn, unpublished results). For this complex nCO ˆ 1982 cm 1 (CH2Cl2),
whereas for analogous complexes with L ˆ PPh3 and P(4-ClC6H4)3
nCO ˆ 1978 and 1984 cm 1: A. Huang, J. E. Marcone, K. L. Mason,
W. J. Marshall, K. G. Moloy, Organometallics 1997, 16, 3377 ± 3380.
[22] J. March, Advanced Organic Chemistry, 4th ed., Wiley, New York,
1992, p. 762.
[*] Dr. R. M. Bullock, Dr. M. Schlaf, Dr. P. Ghosh
Chemistry Department, Brookhaven National Laboratory
Upton, NY 11973-5000 (USA)
Fax : (‡1)631-344-5815
E-mail: bullock@bnl.gov
Dr. P. J. Fagan, Dr. E. Hauptman
The Dupont Company
Central Research and Development Department
Experimental Station
[23] a) C. Bianchini, J. A. Casares, M. Peruzzini, A. Romerosa, F.
Zanobini, J. Am. Chem. Soc. 1996, 118, 4585 ± 4594, and references
therein; b) M. I. Bruce, A. G. Swincer, Aust. J. Chem. 1980, 33, 1471 ±
P. O. Box 80328, Wilmington, DE 19880-0328 (USA)
Â
Ä
1483; c) M. L. Buil, M. A. Esteruelas, A. M. Lopez, E. Onate,
Organometallics 1997, 16, 3169 ± 3177.
[**] We thank the U.S. Department of Energy, Office of Science,
Laboratory Technology Research Program for support. Research at
Brookhaven National Laboratory was carried out under contract DE-
AC02-98CH10886 with the U.S. Department of Energy and was
additionally supported by its Division of Chemical Sciences, Office of
Basic Energy Sciences. We thank Dupont Central Research and
Development for additional funding. M.S. thanks the NSERC
(Canada) for a postdoctoral fellowship.
[24] For relevant proposals about the role of an N-protonated pyridyl-
phosphane ligand (cf. F), see: E. Drent, P. Arnoldy, P. H. M.
Budzelaar, J. Organometal. Chem. 1994, 475, 57 ± 63; A. Scrivanti, V.
Beghetto, E. Campagna, M. Zanato, U. Matteoli, Organometallics
1998, 17, 630 ± 635; M. T. Reetz, R. Demuth, R. Goddard, Tetrahedron
Lett. 1998, 39, 7089 ± 7092.
Angew. Chem. Int. Ed. 2001, 40, No. 20
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